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CHEMISTRY OF THE PLANT VIRUSES
Author(s) -
McFARLANE A. S.
Publication year - 1939
Publication title -
biological reviews
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.993
H-Index - 165
eISSN - 1469-185X
pISSN - 1464-7931
DOI - 10.1111/j.1469-185x.1939.tb00931.x
Subject(s) - ultracentrifuge , chemistry , isoelectric point , crystallinity , analytical ultracentrifugation , tobacco mosaic virus , turnip yellow mosaic virus , homogeneous , virus , molecule , nucleoprotein , precipitin , sedimentation equilibrium , alfalfa mosaic virus , crystallography , plant virus , chromatography , biochemistry , coat protein , virology , biology , organic chemistry , rna , enzyme , physics , gene , antibody , immunology , thermodynamics
Summary 1. By fractional precipitation of the crude sap from virus‐infected plants, or by ultracentrifugation, protein substances are obtained which are capable of transmitting the disease. These proteins may be purified by various methods, notably by incubation with trypsin which selectively digests the impurities. They have high phosphorus contents and behave as nucleoproteins. 2. Examination in the ultracentrifuge reveals that these proteins have larger molecules than any hitherto discovered. In carefully prepared specimens the sedimentation boundaries are those of perfectly homogeneous substances. Sedimentation constants varying from 115times10– 13 to 240times10– 13 have been obtained for different viruses. 3. The viruses are stable inside the range pH 2.0–9.0, although showing often an insolubility zone. They are electrochemically homogeneous inside the stability range with isoelectric points somewhere between pH 3 and 5. 4. One virus, that causing Bushy stunt disease, has a spherical molecule and gives regular crystals. The others are anisotropic and give ill‐defined needles. Purified solutions of the anisotropic viruses show marked birefringence of flow, and this phenomenon in conjunction with X‐ray analysis has been used to obtain estimates of the molecular parameters. In the case of the tobacco mosaic virus the thicknzss of the molecule is 15 mμ . and the length probably 40 times this value. Bushy stunt virus has a diameter of 27 m μ . and a molecular weight of 8,800,000. 5. The crystallinity of the viruses cannot be regarded as a proof of their purity. X‐ray measurements on the crystals show that these have the intramolecular pattern characteristic of proteins. Measurements on semi‐dry films of virus show that in these the molecular rds are closely packed together with very little space for water or any foreign substance between them.